In electrical power transmission and distribution networks, it must always be expected that short circuits can result in island network formation. In an island network, the voltage, frequency and the phase are no longer synchronized to the corresponding parameters in the main network. In particular on reconnection after clearing of the network fault, this can lead to high equalizing currents flowing, which can result in overloading of or damage to components. Furthermore, in the case of conventional power stations with synchronous generators, there is a risk of the discrepancies in the island network becoming so great that the generator will stall on connection to the rest of the network.
Wind energy installations are frequently provided at locations where there is a large amount of wind and the population density is low. In many cases, this results in the wind energy installations having to be connected via relatively long spurs, with only little networking, of a power transmission network. Because of this arrangement, wind energy installations are relatively easily affected by island formation in the network in the event of any disturbance.
This applies both to wind energy installations positioned individually and to a plurality of wind energy installations combined to form a wind farm.
When wind energy installations are arranged in the island network, then the network frequency in them can easily rise relatively quickly. One significant factor in this case is that wind energy installations—in contrast to the synchronous generators which are used in conventional power stations—have only a small mass inertia. Because of the greater discrepancy, equalization processes can occur to a more considerable extent on reconnection, thus resulting in the risk of damage.